The starting point is an environment that is almost 100% virtual (besides the ESXi hosts, obviously). Outlook uses online mode as opposed to Exchange cached mode. To be clear, this is Exchange on-premises, not to be confused with "Exchange Online" (Office 365).

Now let's suppose that the organization moves to Office 365 with Exchange Online (Online with a capital "O").

Client machines will remain virtual and hosted on-premises.

Desktops are persistent. I'm not sure if that will change in the future.

Is it recommended to use Exchange cached mode with Office 365?

On one hand, Outlook working directly with the mailbox in the cloud would seem to require a very low-latency connection to avoid delays.

Side note: it has been made clear that slower Outlook performance would not be acceptable. User experience would have to be "equal or better" than it is now. Current on-premises Exchange / Outlook performance and stability is very good, often described as "rock solid".

On the other hand, I've heard at least one source claim that the time to update the Outlook cache every morning can take a lot of time (as in get up and get some coffee). This was in another environment. I'm not sure how accurate that assertion is and have no idea what kind of Internet connection was involved.

The organization would prefer not to have .ost files several dozen GBs large on the virtual clients.

You really need to have OST files for two major reasons.1. You can't search a mailbox without it2. You really need the performance

Common practice is that you redirect the OST files to a cheap storage, and have a rigorous archiving policy on the mailboxes so they would be as small as possible. Last one depending on how they use their mail__________________Have SpaceSuit, Will Travel

I found KTools software from Google, then go to KTools Support to talked regarding migrate Exchange offline .ost file to Office 365. They provided a tool for migrating Exchange offline .ost file to Office 365. I have had completely imported .ost data to Office 365 account.

Insert Photos

Web address (URL)

Image URL

If your URL is correct, you'll see an image preview here. Large images may take a few minutes to appear.
Remember: Using others' images on the web without their permission may be bad manners, or worse, copyright infringement.